Salvatore babbles on about how good men like him and you are sparse in this world, before getting to the real point. The picket liners of the ferry strike at Portland Harbor has created a problem - Sal can't get his offshore product in. He wants you to meet their Union leader, Jane Hopper, to pay her off and give the Leones 24/7 access to the perimeter.
When you meet Jane Hopper, she couldn't really give a crap about Sal's kind offer, and leaves her boys to finish you off. Your initial reaction is to run for the official exit, but you can just run onto the beach as a fast way to pass the mission.
If you enter the Harbor, before and after this mission, you'll have an infinite horde of picket liners and striking workers to deal with. They'll just keep on regenerating new attackers, so if you want to take your chances for a load of money, you can kill them all and pick up their cash.